Method of polishing

ABSTRACT

This invention describes methods of polishing with pads useful in the manufacture of semiconductor devices or the like. These pads have an advantageous hydrophilic polishing material and have an innovative surface topography and texture which generally improves predictability and polishing performance. These pads provide exceptional performance when used for polishing in conjunction with a slurry in which the abrasive particles are stabilized by use of an amino alcohol. They are also useful when used with slurries comprising an organic polymer.

This application claims the benefit of Provisional Application SerialNo. 60/133,416 filed May 11, 1999.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to the method of use ofpolishing pads with polishing compositions in the manufacture ofsemiconductor devices or the like. More particularly, the polishing padsof the present invention comprise an advantageous hydrophilic materialhaving an innovative surface topography and texture which generallyimproves polishing performance (as well as the predictability ofpolishing performance).

2. Discussion of the Related Art

Integrated circuit fabrication generally requires polishing of one ormore substrates, such as silicon, silicon dioxide, tungsten, copper oraluminum. Such polishing is generally accomplished, using a polishingpad in combination with a polishing fluid.

The semiconductor industry has a need for precision polishing to narrowtolerances, but unwanted “pad to pad” variations in polishingperformance are quite common. A need therefore exists in thesemiconductor industry for polishing pads which exhibit more predicableperformance during high precision polishing operations.

U.S. Pat. No. 5,569,062 describes a cutting means for abrading thesurface of a polishing pad. U.S. Pat. No. 5,081,051 describes anelongated blade having a serrated edge pressing against a pad surface,thereby cutting circumferential grooves into the pad surface. U.S.5,489,233 is directed to a polishing pad having large and small flowchannels produced solely by external means upon the surface of a soliduniform polymer sheet.

During the chemical-mechanical polishing (CMP) of interlayer dielectricsused in the manufacture of integrated circuits a slurry is used inconjunction with a polishing pad to facilitate the removal of aninsulator or dielectric material. In most CMP applications thisinsulating or dielectric material is SiO₂. In an aqueous environment thesurface undergoes a hydration reaction with H₂O to produce a surfacenetwork of hydroxylated Si molecules. Dissolution of this networkgenerally occurs above a pH of 9.0 because of the solubility of thereaction product at high pH. Also, a high pH is desirable to achieve ahigh removal rate. Silicon Nitride, while chemically dissimilar to SiO₂,has shown generally similar polishing behavior. Thus, formulations shownto be suitable for the polishing of SiO₂ are also effective for siliconnitride, albeit at lower rates. To achieve this high pH, bases such asKOH and NH₄OH are used to yield a pH of 10-11 in commercial productionof polishing slurries useful for CMP of insulating layers.

It is imperative in the slurries useful for CMP removal of insulatingmaterials that the dispersions of silicon dioxide particles upon whichthese slurries are based be stable. It is an object of this invention toprovide dispersions of submicron abrasive particles which do not gel orsettle out and, if there is sedimentation, that the sediment be easilyredispersed. A further object of this invention is to provide slurriesuseful for the chemical-mechanical polishing of insulation layers onsemiconductor wafers which are stable and provide a high quality surfacefor the semiconductor wafers upon polishing with the polishing pads ofthis invention.

SUMMARY OF THE INVENTION

The present invention is directed to methods of use of polishing padshaving an innovative hydrophilic polishing layer and also an innovativepolishing surface topography and texture. “Topography” is intended tomean surface characteristics on a scale of less than 10 microns, and“surface texture” is intended to mean surface characteristics of 10microns or more.

The polishing pads of the present invention comprise a random surfacetopography. The random surface topography is preferably achieved bysolidifying or otherwise forming (without cutting) the polishingsurface, rather than cutting or skiving the pad from a larger material.Cutting or skiving causes a blade or other cutting implement to cutsubstantially parallel to the polishing surface being formed; suchcutting tends to create a non-random surface topography, because as theblade cuts the polishing surface, it scores the surface or otherwisecauses pattern on the surface; this pattern generally indicates thedirection of cutting.

It has been surprisingly discovered that for certain high precisionpolishing applications, a non-random surface pattern, due to cutting orskiving, tend to create a relatively high (and unpredictable) number ofundesirable macro-defects. “Macro-defects” are intended to mean burrs orother protrusions from the polishing surface of the pad which have adimension (either width, height or length) of greater than 25 microns.Such macro-defects are detrimental to polishing and can causeperformance variations between pads, because although the cuttingprocess may be substantially the same for each pad, as the cuttinginstrument dulls, the amount of macro-defects created by the cuttinginstrument generally increases. Other factors which can causevariability in macro-defects during cutting include ambient temperature,and line speed variations.

Macro-defects should not be confused with“micro-asperities.”Micro-asperities are intended to mean burrs or otherprotrusions from the polishing surface of the pad which have a dimension(either width, height or length) of less than 10 microns. It has beensurprisingly discovered that micro-asperities are generally advantageousin precision polishing, particularly in the manufacture ofsemi-conductor devices.

The polishing materials of the present invention have no intrinsicability to absorb or transport slurry particles, and therefore thepresent invention does not include felt-based polishing pads created bycoalescing a polymer onto a fiber substrate, as described in U.S. Pat.No. 4,927,432 to Budinger, et al. Furthermore, the polishing materialsof the present invention comprise a hydrophilic material having: i. adensity greater than 0.5 g/cm³; ii. a critical surface tension greaterthan or equal to 34 milliNewtons per meter; iii. a tensile modulus of0.02 to 5 GigaPascals; iv. a ratio of tensile modulus at 30° C. totensile modulus at 60° C. of 1.0 to 2.5; v. a hardness of 25 to 80 ShoreD; vi. a yield stress of 300-6000 psi (2.1-41.4 MegaPascal); vii. atensile strength of 1000 to 15,000 psi (7-105 MegaPascal); and viii. anelongation to break up to 500%. In a preferred embodiment, the polishinglayer further comprises a plurality of soft domains and hard domains.The pads of this invention are particularly effective when they have ahardness of 50 to 80 Shore D and are used in conduction with theslurries of this invention.

The polishing layers of the present invention are manufactured by: 1.molding, embossing, printing, casting, sintering, photo-imaging,chemical etching, solidifying or otherwise creating pads without cuttingthe pad from a larger material; and 2. applying at least a portion of amacro-texture onto (or into) the polishing surface without cutting (orsimilar-type fracturing of) the polishing surface. The method(s) of thepresent invention are directed to causing a flowable material to form(without cutting) a macro-textured into or onto a surface (andoptionally also forming a micro-texture) or alternatively (or inaddition) thereafter inducing a macro-texture upon the polishing surfacewithout cutting or similar type fracturing of the polishing surface,such as, by embossing. Optionally, additional macro-texture (and/ormicro-texture) can thereafter be machined or otherwise cut into thepolishing surface.

Another aspect of the present invention is a method for polishing asemiconductor wafer wherein the surface of said wafer is exposed to apolishing pad of this invention and to a to a polishing compositioncomprising: water, an aqueous dispersion of submicron abrasive particlesfor which an amino alcohol is used as a stabilizing component, and achemically interactive component that interacts with the surface beingpolished.

Another aspect of the present invention is a method for polishing asemiconductor wafer wherein the surface of said wafer is exposed to apolishing pad of this invention and to a to a polishing compositioncomprising an organic polymer having a degree of polymerization of atleast five, said polymer having a plurality of moieties with affinity tosurface groups on said semiconductor wafer surface.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an Atomic Force Microscope (AFM) image of a wafer surfaceafter polishing with Slurry G.

FIG. 2 is an AFM image of a wafer surface after polishing with Slurry H.

FIG. 3 is an AFM image of a wafer surface after polishing with Slurry L.

FIG. 4 is an AFM image of a wafer surface after polishing with Slurry M.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is directed to an improved method of polishingusing a pad useful in the polishing or planarizing of substrates,particularly substrates for the manufacture of semiconductor devices orthe like. The compositions and methods of the present invention may alsobe useful in other industries and can be applied to any one of a numberof materials, including but not limited to silicon, silicon dioxide,metal, dielectrics (including polymeric dielectrics), ceramics andglass.

Macro defects (large surface defects of 25 microns or more due tofractures, abrasions and/or similar-type surface irregularities,generally arising from the cutting of a macro-texture into a pad) mustbe distinguished from micro asperities (small surface protrusions of 10microns or less due to surface fractures, abrasion and/or similar-typesurface irregularities, generally arising from the cutting of amicro-texture into a pad). Macro-texture and micro-texture provide verydifferent functions for a polishing pad. The macro-texture provides apassageway (or a series of passageways) for distributing polishing fluidalong the pad surface. The micro-texture can be very similar to themacro-texture, but on a much smaller scale.

Unlike the (much larger) macro-texture, the micro-texture is on a scalesimilar to that of the surface protrusions being polished away. Themicro-texture provides an environment which enhances interactionbetween: 1. the polishing fluid and/or polishing particles; and 2. theprotrusions to be polished away.

The present invention is innovative in its recognition that: 1.micro-asperities are generally beneficial to the polishing performanceof a pad; and 2. macro-defects are generally detrimental to polishingperformance of a pad. The present invention is also innovative inaddressing the adverse affects of macro-defects by solidifying orotherwise forming or molding at least a portion of the macro-textureinto or onto the polishing surface, macro-defects are dramaticallyreduced and pad performance is improved, relative to conventional padsproduced by cutting a macro-texture into a pad.

In conventional pad manufacturing processes, mechanical cuttingoperations are used:

1. to cut pads from a polymer cake; or

2. to cut or otherwise machine a macro-texture into a pad.

The number of macro-defects can be dependent upon the sharpness of thecutting tool, line speed, ambient temperature/humidity and the like.This will tend to cause pad-to-pad variation in macro-defects which inturn will cause pad-to-pad variation in polishing performance.

The pads of the present invention comprise a polishing layer having anouter surface. Preferred processes in accordance with the presentinvention include: 1. thermoplastic injection molding, 2. thermosetinjection molding (often referred to as “reaction injection molding” or“RIM”), 3. thermoplastic or thermoset injection blow molding, 4.compression molding, or 5. any similar-type process in which a flowablematerial is positioned and solidified, thereby creating at least aportion of a pad's macro-texture. In a preferred molding embodiment ofthe present invention: 1. the flowable material is forced into or onto astructure or substrate; 2. the structure or substrate imparts a surfacetexture into the material as it solidifies; and 3. the structure orsubstrate is thereafter separated from the solidified material.

In one embodiment of the manufacture of pads useful in the methods ofthis invention, a solid or semi-solid insert is first placed in anenclosure, and the flowable material is then forced into the enclosure,thereby causing the insert to be bonded to or within the material afterit has solidified. The insert can provide reinforcement to the pad sothat the solidified material around the insert need not beself-supporting or otherwise of a consistency necessary to support thepolishing layer. Alternatively or in addition, the insert can providestructural integrity to the pad, thereby providing improved performance,longevity and/or greater flexibility in manufacturing.

Machining a groove or indentation into a pad disrupts the pad's surface,causing fracturing, abrasion, irregularities or otherwise macro-defectsto the pad surface; in the precision polishing required in thesemiconductor industry, such macro-defects (due to machining amacro-texture into a polishing pad) can be detrimental to padperformance (particularly predictability). By flowing and solidifying(e.g., molding) at least a portion of the macro-texture into (or onto)the pad polishing layer (without cutting) in accordance with the presentinvention, the polishing layer surface is far less disturbed or damaged(relative to machining); therefore the pads of the present inventionwill exhibit fewer macro-defects, and pad polishing performance andpredictability of pad performance, are generally improved.

Although molding technology useful in accordance with the presentinvention is quite common in many industries, the molding of the presentinvention involves an average mold aspect ratio of at least 400, morepreferably at least 500 and yet more preferably greater than 700.

The “aspect ratio” is intended to mean a selected length divided by theaverage thickness of the pad.

Molding a precision polishing pad with such a high aspect ratio iscontrary to prevailing views in the industry and can be difficult, ifnot impossible, depending upon the pad material selected. As a result,polishing pads have been manufactured by other manufacturing operations,such as by coagulating polymer onto felt substrates or by casting apolymeric material into cakes (which are then skived to produce apolishing pad), because the advantages of the present invention have notbeen appreciated by those of ordinary skill in the art.

Surprisingly, the preferred pad compositions of the present inventioncan be molded in accordance with the present invention to providepolishing pads which are able to satisfy needs which are not otherwiseobtainable with common prior art pad manufacturing processes. Forexample, the pads of the present invention are generally more preciseand reproducible, relative to many conventional pad manufacturingprocesses.

Pads are generally conditioned prior to use. The conditioning creates oraugments the micro-texture of the pad. During use, the micro-texture canexperience unwanted plastic flow and can be fouled by debris. As aresult, pads are generally re-conditioned periodically during theiruseful life to regenerate an optimal micro-texture. In some embodiments,the polishing pads of the present invention require less re-conditioningduring use, relative to conventional polishing pads.

In a preferred embodiment, the pad's macro-structure is incorporatedinto the surface of the polishing layer, due to the presence of moldprotrusions around which pad material initially flows and solidifies. Inthis way, the macro-texture can be simultaneously created along thepolishing layer's outer surface as the pad material solidifies. Themacro-texture preferably comprises one or more indentations having anaverage depth and/or width of greater than 0.01, more preferably 0.05and yet more preferably 0.1 millimeters. This macro-texture facilitatesthe flow of polishing fluid and thereby enhances polishing performance.

A preferred process of the present invention is directed to injectionmolding, particularly “reaction injection molding” or “RIM”. RIMgenerally involves mixing reactive liquid (or semi-liquid) precursorswhich are then rapidly injected into the mold. Once the mold is filled,the reactive precursors proceed with a chemical reaction, causingsolidification of a final molded product. This type of injection moldingis most preferred, because the pad's physical properties can be finetuned by adjusting the reactive chemistry. In addition, reactioninjection molding generally uses lower viscosity precursors thanthermoplastic injection molding, thereby allowing for easier filling ofhigh aspect ratio molds.

Urethane prepolymers are a preferred reactive chemistry for reactioninjection molding in accordance with the present invention.“Prepolymers” are intended to mean any precursor to the finalpolymerized product, including oligomers or monomers. Many suchprepolymers are well known and commercially available. Urethaneprepolymers generally comprise reactive moieties at the ends of theprepolymer chains.

A common reactive moiety for a urethane prepolymer is isocyanate.Commercially available isocyanate prepolymers include di-isocyanateprepolymers and tri-isocyanate prepolymers. Examples of di-isocyanatepolymers include toluene diisocyanate and methylene diisocyanate. Theisocyanate prepolymer preferably comprises an average isocyanatefunctionality of at least two. An average isocyanate functionalitygreater than 4 is generally not preferred, since processing can becomedifficult, depending upon the molding equipment and process being used.

The isocyanate prepolymer is generally reacted to a second prepolymerhaving an isocyanate reactive moiety. Preferably, the second prepolymercomprises, on average, at least two (2) isocyanate reactive moieties.Isocyanate reactive moieties include amines, particularly primary andsecondary amines, and polyols; preferred prepolymers include diamines,diols and hydroxy functionalized amines. In addition, abrasive particlesmay be incorporated into the pad material. De-watered polishing fluid orany precursor to a polishing fluid may be incorporated into the pad,whereby during polishing, as water is placed within the polishinginterface and the pad wears, the pad provides constituents to create orimprove the polishing fluid.

Any prepolymer chemistry however could be used in accordance with thepresent invention, including polymer systems other than urethanes,provided the final product exhibits the following properties: a densityof greater than 0.5g/cm³, more preferably greater than 0.7g/cm³ and yetmore preferably greater than about 0.9g/cm³; a critical surface tensiongreater than or equal to 34 milliNewtons per meter; a tensile modulus of0.02 to 5 GigaPascals; a ratio of the tensile modulus at 30° C. to themodulus at 60° C. in the range of 1.0 to 2.5; hardness of 25 to 80 ShoreD; a yield stress of 300 to 6000 psi; a tensile strength of 500 to15,000 psi, and an elongation to break up to 500%. These properties arepossible for a number of materials useful in injection molding andsimilar-type processes, such as: polycarbonate, polysulphone, nylon,ethylene copolymers, polyethers, polyesters, polyether-polyestercopolymers, acrylic polymers, polymethyl methacrylate, polyvinylchloride, polycarbonate, polyethylene copolymers, polyethylene imine,polyurethanes, polyether sulfone, polyether imide, polyketones, and thelike, including photochemical reactive derivatives thereof.

A catalyst is often necessary to decrease the polymerization reactiontime, particularly the gel time and the de-mold time. However, if thereaction is too fast, the material may solidify or gel prior to completefilling of the mold. Gel time is preferably in the range of a halfsecond and one hour, more preferably in the range of about 1 second andabout 5 minutes, more preferably 10 seconds to 5 minutes, and yet morepreferably 30 seconds to 5 minutes.

Preferred catalysts are devoid of transition metals, particularly zinc,copper, nickel, cobalt, tungsten, chromium, manganese, iron, tin, orlead. The most preferred catalyst for use with a urethane prepolymersystem comprises a tertiary amine, such as, diazo-bicyclo-octane. Otheruseful catalysts include, organic acids, primary amines and secondaryamines, depending upon the particular reactive chemistry chosen.

In a preferred embodiment, the pad material is sufficiently hydrophilicto provide a critical surface tension greater than or equal to 34milliNewtons per meter, more preferably greater than or equal to 37 andmost preferably greater than or equal to 40 milliNewtons per meter.Critical surface tension defines the wettability of a solid surface bynoting the lowest surface tension a liquid can have and still exhibit acontact angle greater than zero degrees on that solid. Thus, polymerswith higher critical surface tensions are more readily wet and aretherefore more hydrophilic. Critical Surface Tension of common polymersare provided below:

Polymer Critical Surface Tension (mN/m) Polytetrafluoroethylene 19Polydimethylsiloxane 24 Silicone Rubber 24 Polybutadiene 31 Polethylene31 Polystyrene 33 Polypropylene 34 Polyester 39-42 Polyacrylamide 33-40Polyvinyl alcohol 37 Polymethyl methacrylate 39 Polyvinyl chloride 39Polysulfone 41 Nylon 6 42 Polyurethane 45 Polycarbonate 45

In one embodiment, the pad matrix is derived from at least:

1. an acrylated urethane;

2. an acrylated epoxy;

3. an ethylenically unsaturated organic compound having a carboxyl,benzyl, or amide functionality;

4. an aminoplast derivative having a pendant unsaturated carbonyl group;

5. an isocyanurate derivative having at least one pendant acrylategroup;

6. a vinyl ether,

7. a urethane

8. a polyacrylamide

9. an ethylene/ester copolymer or an acid derivative thereof;

10. a polyvinyl alcohol;

11. a polymethyl methacrylate;

12. a polysulfone;

13. an polyamide;

14. a polycarbonate;

15. a polyvinyl chloride;

16. an epoxy;

17. a copolymer of the above; or

18. a combination thereof.

Preferred pad materials comprise urethane, carbonate, amide, sulfone,vinyl chloride, acrylatc, methacrylate, vinyl alcohol, ester oracrylamide moieties. The pad material can be porous or non-porous. Inone embodiment, the matrix is non-porous; in another embodiment, thematrix is non-porous and free of fiber reinforcement.

In a preferred embodiment, the polishing layer material comprises: 1. aplurality of rigid domains which resists plastic flow during polishing;and 2. a plurality of less rigid domains which are less resistant toplastic flow during polishing. This combination of properties provides adual mechanism which has been found to be particularly advantageous inthe polishing of silicon dioxide and metal. The hard domains tend tocause the protrusion to rigorously engage the polishing interface,whereas the soft domains tend to enhance polishing interaction betweenthe protrusion and the substrate surface being polished.

The rigid phase size in any dimension (height, width or length) ispreferably less than 100 microns, more preferably less than 50 microns,yet more preferably less than 25 microns and most preferably less than10 microns. Similarly the non-rigid phase is also preferably less than100 microns, more preferably less than 50 microns, more preferably lessthan 25 microns and most preferably less than 10 microns. Preferred dualphase materials include polyurethane polymers having a soft segment(which provides the non-rigid phase) and a hard segment (which providesthe rigid phase). The domains are produced during the forming of thepolishing layer by a phase separation, due to incompatibility betweenthe two (hard and soft) polymer segments.

Other polymers having hard and soft segments could also be appropriate,including ethylene copolymers, copolyester, block copolymers,polysulfones copolymers and acrylic copolymers. Hard and soft domainswithin the pad material can also be created: 1. by hard and softsegments along a polymer backbone; 2. by crystalline regions andnon-crystalline regions within the pad material; 3. by alloying a hardpolymer with a soft polymer; or 4. by combining a polymer with anorganic or inorganic filler. Useful such compositions includecopolymers, polymer blends interpenetrating polymer networks and thelike.

The pads of the present invention are preferably side-filled byinjecting the pad material into the mold at a point along the peripheryof the mold. Pads may also be center filled by injecting flowablematerial into the mold at or near the geometric center of a mold face.

A preferred method of creating the macro-channels or macro-indentationsis by molding, particularly injection molding, whereby the macro-textureis formed in situ by one or more thin-walled protrusions extending intothe mold. The mold protrusions preferably provide an inverted imagewhich is complementary to the intended macro-texture design orconfiguration. Injection molding is a well known technology and need notbe described further here. The macro-indentation(s) is(are) useful inproviding large flow channels for the polishing fluid, during thepolishing operation.

An agent comprising a wax, hydrocarbon or other solid, semi-solid orliquid organic material can be applied to the mold to enhance release ofthe molded part after molding. A preferred mold release agent comprisesa solid organic material and a solvent or liquid carrier. A particularlypreferred mold release agent is a fluorocarbon dispersion, availablefrom E. I. du Pont de Nemours and Company, Wilmington, Del., USA.Preferred solvents or liquid carrier materials have a vapor pressure inthe range of 0.1 to 14.7 pounds per square inch (“psi”), more preferably1-12 psi and yet more preferably in the range of 4.5 to 5.5 psi. In apreferred embodiment, a wax, hydrocarbon or other non-polar solidorganic material is dissolved or suspended in an organic solvent,preferably a non-polar organic solvent, such as mineral spirits, andapplied as a mold release agent prior to the injection operation.Alternatively, an internal mold release agent can be used, which isincorporated directly into the pad material and aids in de-molding thepad after pad manufacture.

Pad surface topography is relatively consistent for pads of the presentinvention, because the mold surface remains generally the same for eachpad produced by it. Pads produced by many conventional methods aregenerally more prone to variations and inconsistencies. Predictabilityof performance is an important aspect of a precision polishing pad. Padconsistency allows for more exacting standard operating procedures andtherefore more productive (and reproducible) polishing operations.

After forming the pad's polishing layer, including at least a part ofthe macro-texture, the outer surface can be further modified by adding amicro-texture. The micro-texture is preferably created by moving thepolishing layer surface against the surface of an abrasive material. Inone embodiment, the abrasive material is a rotating structure (theabrasive material can be round, square, rectangular, oblong or of anygeometric configuration) having a plurality of rigid particles embedded(and preferably, permanently affixed) upon the surface. The movement ofthe rigid particles against the pad surface causes the pad surface toundergo plastic flow, fragmentation or a combination thereof (at thepoint of contact with the particles). The abrasive surface need notrotate against the pad surface; the abrasive surface can move againstthe pad in any one of a number of ways, including vibration, linearmovement, random orbitals, rolling or the like.

The resulting plastic flow, fragmentation or combination thereof (due tothe abrasive surface), creates a micro-texture upon the pad's outersurface. The micro-texture can comprise a micro-indentation with amicro-protrusion adjacent to at least one side. In one embodiment, themicro-protrusions provide at least 0.1 percent of the surface area ofthe pad's polishing surface, and the micro-indentations have an averagedepth of less than 50 microns, more preferably less than 10 microns, andthe micro-protrusions have an average height of less than 50 microns andmore preferably less than 10 microns. Preferably, such surfacemodification with an abrasive surface will cause minimal abrasionremoval of the polishing layer, but rather merely plows furrows into thepad without causing a substantial amount, if any, of pad material toseparate from the polishing layer. However, although less preferred,abrasion removal of pad material is acceptable, so long as amicro-texture is produced.

In an alternative embodiment, at least a portion of themicro-indentations or micro-protrusions may also be created during themolding process by incorporation of appropriate features into the mold.Formation of micro-texture and macro-texture during the fabrication ofthe pad can diminish or even negate the necessity of preconditioningbreak-in. Such formation also provides more controlled and faithfulreplication of the micro-texture as compared to surface modificationsubsequent to pad creation.

The pads of the present invention are preferably used in combinationwith a polishing fluid, such as a polishing slurry, for such processesas chemical mechanical polishing of a metal, silicon or silicon dioxidesubstrate. During polishing, the polishing fluid is placed between thepad's polishing surface and the substrate to be polished. As the pad ismoved relative to the substrate being polished, the micro-indentationsallow for improved polishing fluid flow along the interface (between thepad and the substrate to be polished). The improved flow of polishingfluid generally allows for more efficient and effective polishingperformance. Also, during polishing, the substrate and the polishinglayer are pressed against each other, most usually using a pressurebetween the substrate and the polishing layer of greater than 0.1kilograms per square meter.

The pads of the present invention have been found to be particularlyuseful when used in conjunction with polishing fluids in which abrasiveparticles have been dispersed with a dispersing agent from a class ofcompounds known as amino alcohols. Amino alcohols are defined as organiccompounds which contain at least one amino group and one hydroxyl group.To provide stability amino alcohols may be used at 0.01% to 10% byweight in the aqueous dispersions of submicron abrasive particlesaccording to this invention. Submicron abrasive particles which might bestabilized with the amino alcohols include, but are not limited to,silica, ceria, alumina, titania, and silica gel. The submicron abrasiveparticles should have a primary particle size in the range of 5nanometers to 100 nanometers. Primary particle size can be determined byTEM imaging where the smallest particles are measured even if shown aspart of an agglomeration.

It has also been shown that pads of this invention are particularlyuseful when used in conjunction with a polishing fluid which contains asmall amount of an organic polymer having a degree of polymerization ofat least five with a plurality of moieties having affinity to surfacegroups contained on insulating layer surfaces. These groups are commonlypolar moieties, such as, but not limited to, hydroxy, carboxy, carbonyl,alkoxy, sulphonyl, and phosphonyl. Examples of this type of moleculeinclude poly-vinyl alcohol, poly-vinylpyrrolidone, poly-methylmethacrylate, poly-formaldehyde, poly-ethylene oxide, poly-ethyleneglycol, and poly-methacrylic acid. This additive is disclosed in Pat.application Ser. No. 09/329,225 which is made a part of thisspecification by reference. In the previous application, the additivewas made a part of the CMP slurry to provide silica rate suppression.The polymer additive in the present invention provides a polishedsurface with less surface roughness and fewer scratches.

Since at least some of the macro-texture is not created by an externalmeans (such as by machining), the macro-texture is less prone tomacro-defects, such as burrs or protrusions. This has been found toimprove polishing pad performance by providing a polishing surfacehaving very low levels of macro-defects and by substantially diminishingdebris trapped in the macro-indentations that would otherwise inhibitthe flow of polishing fluid.

In use, the pads of the present invention are preferably attached to aplaten and then brought sufficiently proximate with a workpiece to bepolished or planarized. Surface irregularities are removed at a ratewhich is dependent upon a number of parameters, including: pad pressureon the workpiece surface (or vice versa); the speed at which the pad andworkpiece move in relation to one another; and the components of thepolishing fluid.

As the pad polishes, the micro-texture can experience abrasion removalor plastic flow (the micro-protrusions are flattened or are otherwiseless pronounced), which can diminish polishing performance. Themicro-protrusions are then preferably re-formed with furtherconditioning, such as by moving the pad against an abrasive surfaceagain and causing the material to once again form furrows. Suchreconditioning is generally not as rigorous and/or not required as oftenfor pads of the present invention, relative to may common prior artpads.

The preferred abrasive surface for conditioning is a disk which ispreferably metal and which is preferably embedded with diamonds of asize in the range of 1 micron to 0.5 millimeters. During conditioning,the pressure between the conditioning disk and the polishing pad ispreferably between 0.1 to about 25 pounds per square inch. The disk'sspeed of rotation is preferably in the range of 1 to 1000 revolutionsper minute.

A preferred conditioning disk is a four inch diameter, 100 grit diamonddisk, such as the RESI™ Disk manufactured by R. E. Science, Inc. Optimumconditioning was attained when the downforce was 10 lbs per square inch,platen speed was 75 rpm, the sweep profile was bell-shaped, the numberof preconditioning break-in sweeps was 15 and the number of replenishingconditioning sweeps between wafers was 15.

Optionally, conditioning can be conducted in the presence of aconditioning fluid, preferably a water based fluid containing abrasiveparticles.

The polishing fluid is preferably water based and may or may not requirethe presence of abrasive particles, depending upon the composition ofthe polishing layer. For example, a polishing layer comprising abrasiveparticles may not require abrasive particles in the polishing fluid.

EXAMPLES

Examples 1 and 2 are comparative examples. Example 3 illustrates padsuseful in the present invention. Example 4 shows the results ofpolishing an insulation layer with pads and slurries of this invention.

(Comparative) Example 1

A polymeric matrix was prepared by mixing 2997 grams of polyether-basedliquid urethane with 768 grams of 4, 4-methylene-bis-chloroaniline atabout 1 50° F. At this temperature, the urethane/polyfunctional aminemixture has a pot life of about 2.5 minutes; during this time, about 69grams of hollow elastic polymeric microspheres were blended at 3450 rpmusing a high shear mixer to evenly distribute the microspheres in themixture. The final mixture was transferred to a conventional mold andpermitted to gel for about 15 minutes.

The mold was then placed in a curing oven and cured for about 5 hours atabout 200° F. The mixture was then cooled for about 4-6 hours, until themold temperature was about 70° F. The molded article was then “skived”into thin sheets and macro-channels mechanically machined into thesurface. The machining process produced jagged, irregular grooves withsurface burrs.

A four inch diameter, 100 grit diamond disk was used to producemicro-channels and micro-protrusions on the surface of the pad. The diskwas a RESI™ Disk manufactured by R. E. Science, Inc. Conditioning wasaccomplished with a downward force of about 10 lbs., a platen speed of75 rpm, a bell-shaped sweep profile, and about 15 sweeps.

(Comparative) Example 2

This example used the same manufacturing process as Example 1 but thepolyurethane was unfilled. By eliminating the filler, the pad propertiesare generally more reproducible; however, since the pads are now harder,machining problems are found to be greater.

Example 3

Instead of separate skiving and machining steps, polyurethaneformulations similar to those used in Examples 1 and 2 were formed intoa pad by injection molding into a mold having the complementary finaldimensions and groove design of the desired pad. This is a net-shapeprocess, eliminating the need for separate skiving and groovingoperations.

The resultant pads of this example (Example 3) had less part-to-partvariability in thickness and groove dimensions, and the grooves weresubstantially free of macro-defects (e.g., burrs). During oxide CMPpolishing, fewer defects upon the substrate were induced. The pad'suseful life was increased, because there was less need for padconditioning between wafers.

Modulus Ratio Pad Type/Parameter Pad Lifetime Defectivity E(30°C.):E(60° C.) Example 1:  300 wafers baseline 2.0-2.5 Example 2:  400wafers 5 × baseline 2.0-2.5 Example 3: Present 1200 wafers 0.1 ×baseline 1.3-2.0 Invention

Example 4

Polishing tests on TEOS wafers shown below in Table 2 were carried outon a Strasbaugh 6DS-SP polisher under the following conditions: Time,120 sec; Down force, 7 psi; Back pressure, 0.5 psi; Platen speed, 51rpm; Carrier speed, 41 rpm; Temperature, ambient; Slurry flow, 125ml/min; Slurry dilution ratio, 1:1 with DI water; Pad type, a padaccording to Example 3 in which the polyurethane is unfilled.

TABLE 2 Roughness Composition SiO₂ RR RMS P-V Slurry Weight % Å/min nmnm G 25% A-70, 1.7% TA, 0.38% KOH 1800 .30 3.9 H G + 0.2% PVP 1800 .263.9 L 20% A-130, 1% TA, 0.36% KOH 1600 .42 5.2 M L + 0.2% PVP 1900 .285.0 A-70 = fumed silica powder with a surface area of 70-100 m²/g TA =Tris(hydroxymethyl)aminomethane PVP = poly-vinylpyrrolidone. A-130 =fumed silica powder with a surface area of 120-140 m²/g

The above table shows the improvement in surface roughness of aninsulating layer on the surface of a semiconductor wafer which occursupon addition of an organic polymer (PVP) to a CMP slurry used inconjunction with a pad of this invention when polishing the surface ofthe semiconductor wafer. The surface measurements were obtained using anAtomic Force Microscope (AFM) available from Digital Instruments, Inc.Using the tapping mode, a silicon tip, and a measurement area of 10microns by 10 microns, the root mean square (RMS) roughness and the peakto valley (P-V) roughness were determined. Surface condition can beobserved from the images provided by the AFM. FIGS. 1 to 4 show AFMimages of the wafer surfaces after polishing with slurries G, H, L, andM. These images dramatically show the improvement in surface conditionwhen using an organic polymer in the slurries. Such a polymer wouldtypically be used in concentrations of 0.01% to 5% in the slurries ofthis invention.

Nothing from the above discussion is intended to be a limitation of anykind with respect to the present invention. All limitations to thepresent invention are intended to be found only in the claims, asprovided below.

What is claimed is:
 1. A method of polishing a semiconductor wafer, comprising: a) providing a polishing pad having a polishing layer, said polishing layer consisting essentially of a hydrophilic polishing layer having no intrinsic ability to absorb a plurality of slurry particles, said polishing layer having a polishing surface consisting essentially of a polishing material having: i. a density greater than 0.5 g/cm³; ii. a critical surface tension greater than or equal to 34 milliNewtons per meter; iii. a tensile modulus of 0.02 to 5 GigaPascals; iv. a ratio of tensile modulus at 30° C. to tensile modulus at 60° C. of 1.0 to 2.5; v. a hardness of 25 to 80 Shore D; vi. a yield stress of 300-6000 psi; vii. a tensile strength of 1000 to 15,000 psi; and viii. an elongation to break less than or equal to 500%, said polishing material comprising at least one moiety from the group consisting of: a urethane produced by a catalyst which accelerates an isocyanate reaction, said catalyst being devoid of copper, tungsten, iron or chromium; a carbonate; an amide; an ester; an ether; an acrylate; a methacrylate; an acrylic acid; a methacrylic acid; a sulphone; an acrylamide; a halide; and a hydroxide, said polishing surface having a random surface topography and having a macro-texture produced by solidifying a flowable material, and b) chemical mechanical polishing said semiconductor wafer with said pad and with a polishing composition comprising: water, an aqueous dispersion of submicron abrasive particles for which an amino alcohol is used as a stabilizing component, and a chemically interactive component that interacts with the surface being polished.
 2. A method in accordance with claim 1, wherein said macro-texture is incorporated into the polishing surface due to: i. compression by positive or negative pressure; ii. molding; iii. printing; iv. casting; v. sintering; vi. photo-imaging; or vii. chemical etching.
 3. A method in accordance with claim 2, wherein the polishing pad is formed by reaction injection molding.
 4. A method in accordance with claim 1, wherein the polishing surface is conditioned to create a plurality of micro-asperities by moving an abrasive medium against the polishing surface, said abrasive medium carrying a plurality of rigid particles.
 5. A method in accordance with claim 1, wherein the polishing pad has a Shore D hardness of between 50 and
 80. 6. A method in accordance with claim 1, wherein said amino alcohol is tris(hydroxymethyl)aminomethane.
 7. A method of polishing a semiconductor wafer, comprising: a) providing a polishing pad having a polishing layer, said polishing layer consisting essentially of a hydrophilic polishing layer having no intrinsic ability to absorb a plurality of slurry particles, said polishing layer having a polishing surface consisting essentially of a polishing material having: i. a density greater than 0.5 g/cm³; ii. a critical surface tension greater than or equal to 34 milliNewtons per meter; iii. a tensile modulus of 0.02 to 5 GigaPascals; iv. a ratio of tensile modulus at 30° C. to tensile modulus at 60° C. of 1.0 to 2.5; v. a hardness of 25 to 80 Shore D; vi. a yield stress of 300-6000 psi; vii. a tensile strength of 1000 to 15,000 psi; and viii. an elongation to break less than or equal to 500%, said polishing material comprising at least one moiety from the group consisting of: a urethane produced by a catalyst which accelerates an isocyanate reaction, said catalyst being devoid of copper, tungsten, iron or chromium; a carbonate; an amide; an ester; an ether; an acrylate; a methacrylate; an acrylic acid; a methacrylic acid; a sulphone; an acrylamide; a halide; and a hydroxide, said polishing surface having a random surface topography and having a macro-texture produced by solidifying a flowable material, and b) chemical mechanical polishing said semiconductor wafer with said pad and with a polishing composition comprising an organic polymer having a degree of polymerization of at least five, said polymer having a plurality of moieties with affinity to surface groups on said semiconductor wafer.
 8. A method in accordance with claim 7, wherein said macro-texture is incorporated into the polishing surface due to: i. compression by positive or negative pressure; ii. molding; iii. printing; iv. casting; v. sintering; vi. photo-imaging; or vii. chemical etching.
 9. A method in accordance with claim 7, wherein the polishing surface is conditioned to create a plurality of micro-asperities by moving an abrasive medium against the polishing surface, said abrasive medium carrying a plurality of rigid particles.
 10. A method in accordance with claim 8, wherein the polishing pad is formed by reaction injection molding.
 11. A method in accordance with claim 7 wherein said organic polymer is from the group of poly-vinyl alcohol, poly-vinylpyrrolidone, poly-methyl methacrylate, poly-formaldehyde, poly-ethylene oxide, poly-ethylene glycol, and poly-methacrylic acid.
 12. A method in accordance with claim 11 wherein said organic polymer is poly-vinylpyrrolidone. 